In organic synthesis reactions, the chiral phosphine-nitrogen ligand of the containing amido coordination group is one of the most important chiral ligands. Such chiral phosphine-nitrogen ligands can coordinate with many transition metals to form chiral catalysts that are of great use in the asymmetric catalytic reaction. At present, such transition metal catalysts of chiral phosphine-nitrogen ligand containing amido coordination group have shown excellent reaction activity and enantioselectivity in a large number of asymmetric catalytic reactions (Amoroso, D.; Graham, T. W.; Guo, R.; Tsang, C.-W.; Abdur-Rashid, K. Aldrich. Chimica Acta. 2008, 41, 15).
More recently, due to the development of highly efficient chiral ruthenium-diphosphine/diamine catalysts by Noyori et al. ((a) Ohkuma, T.; Ooka, H.; Hashiguchi, S.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1995, 117, 2675; (b) Ohkuma, T.; Koizumi, M.; Doucet, H.; Pham, T.; Kozawa, M.; Murata, K.; Katayama, E.; Yokozawa, T.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1998, 120, 13529), extremely high catalytic activity and enantioselectivity have been achieved in the asymmetric hydrogenation reaction of non-functionalized ketones which is quite difficult in the past, resulting in close attention to such chiral catalysts. Although quite high enantioselectivity (>99% ee) and reaction activity (S/C>100,000) have been realized in a series of asymmetric catalytic hydrogenations of aromatic ketones, heterocyclic aromatic ketones, α,β-unsaturated ketones by such chiral catalysts, excellent result can be obtained only if the chiral and stereoscopic effect of the chiral diphosphine ligand and diamine ligand are both precisely matched. Therefore, in recent years, research has been focused on the chiral amidophosphine ligand containing amido group, especially containing hydrogen atom on the nitrogen atom, with advantages such as simple synthesis, flexible coordination and having the features of chiral phosphine ligand and amido ligand.
A series of amidophosphine ligands containing NH2 coordination group have been reported by Morris et al. From University of Toronto, Canada in around 2004, and better hydrogenation has been accomplished by the ruthenium complexes with these chiral ligands in the asymmetric catalytic hydrogenation of ketones, imides etc. ((a) Abdur-Rashid, K.; Guo, R.; Lough, A. J.; Morris, R. H.; Song, D. Adv. Synth. Catal. 2005, 347, 571; (b) Guo, R.; Lough, A. J.; Morris, R. H.; Song, D. Organometallics, 2004, 23, 5524; (c) Guo, R.; Morris, R. H.; Song, D. J. Am. Chem. Soc. 2005, 127, 516). It has been reported by Chen's group from University of Liverpool, UK that moderate enantioselectivity (<79% ee) has been achieved in the asymmetric catalytic hydrogenation reaction of aryl alkyl ketones catalyzed by the ruthenium complex with chiral amidophosphine ligand having ferrocene skeleton (Chen, W.; Mbafor, W.; Roberts, S. M.; Whittall, J. Tetrahedron: Asymmetry, 2006, 17, 1161). It has also been reported by Dahlenburg's group from University of Erlangen-Nuremberg, Germany that moderate ee value was obtained in the simple ketone hydrogenation reaction catalyzed by iridium, rhodium complex with chiral amidophosphine ligand derived from β-amido alcohols ((a) Dahlenburg, L.; Götz, R. Eur. J. Inorg. Chem. 2004, 888; (b) Dahlenburg, L.; Gotz, R. Inorg. Chem. Commun. 2003, 6, 443). However, the enantioselectivity of these reported chiral catalysts of the chiral amidophosphine ligands in the asymmetric catalytic hydrogenation of simple ketones is much inferior to those chiral ruthenium-diphosphine/diamine catalysts developed by Noyori et al.
Recently, a series of bidentate chiral spiro-amidophosphine ligands containing aromatic amido group has been designed and synthesized by our group (Jian-Bo Xie, Jian-Hua Xie, Xiao-Yan Liu, Wei-Ling Kong, Shen Li, Qi-Lin Zhou, J. Am. Chem. Soc. 2010, 132, 4538; Qi-Lin Zhou, Jian-Hua Xie, Jian-Bo Xie, Li-Xin Wang, C N 101671365A). Better reaction activity and enantioselectivity have been achieved in the asymmetric catalytic hydrogenation of α,β-unsaturated ketones having exocyclic double bond by the iridium catalysts with such chiral amidophosphine ligands compared with the chiral ruthenium-diphosphine/diamine catalyst; excellent performance has also been observed in the asymmetric catalytic hydrogenation of simple aryl alkyl ketones. However, for this catalyst, the conversion number is still relatively low; although its conversion number (the ratio of substrate to catalyst) in the catalytic hydrogenation reaction of simple ketones and α,β-unsaturated ketones is much higher than that of other chiral catalysts, the maximum value is only 10,000, which is still needed to be further improved.
In the field of asymmetric catalytic hydrogenation reaction, there are only a few chiral catalysts developed with truly high efficiency. The development of highly efficient chiral ligand with simple synthesis and flexible coordination as well as its catalyst remains difficult and challenge in the asymmetric catalysis area.